Integrated circuitry

ABSTRACT

Disclosed are methods of forming resistors and diodes from semiconductive material, and static random access memory (SRAM) cells incorporating resistors, and to integrated circuitry incorporating resistors and diodes. A node to which electrical connection is to be made is provided. An electrically insulative layer is provided outwardly of the node. An opening is provided in the electrically insulative layer over the node. The opening is filled with semiconductive material which depending on configuration serves as one or both of a vertically elongated diode and resistor.

RELATED PATENT DATA

This patent resulted from a continued prosecution application (CPA) ofU.S. patent application Ser. No. 08/692,043, filed Aug. 1, 1996 entitled“A Method of Making a Resistor, Method of Making a Diode, and SRAMCircuitry and Other Integrated Circuitry”, naming J. Brett Rolfson andH. Montgomery Manning as inventors, and which is now U.S. Pat. No.5,825,074 the disclosure of which is incorporated by reference andoriginally filed as a divisional patent application on Aug. 1, 1996.That patent resulted from a divisional application of U.S. patentapplication Ser. No. 08/528,124, filed on Sep. 14, 1995 and now U.S.Pat. No. 5,567,644, entitled “Method of Making A Resistor, Method ofMaking A Diode, And SRAM Circuitry And Other Integrated Circuitry”listing as inventors: J. Brett Rolfson and Monte Manning.

TECHNICAL FIELD

This invention relates generally to semiconductor processing methods offorming resistors and diodes from semiconductive material, and to staticrandom access memory (SRAM) cells incorporating resistors, and to otherintegrated circuitry incorporating resistors and diodes.

BACKGROUND OF THE INVENTION

One of the common elements required in electrical circuit devices is thepull-up or pull-down resistor from an active device to one of the supplybuses, typically referred to as Vcc. The pull-up is simple if used toconstruct a circuit using discrete components in that all that isrequired is selecting a resistor of the desired resistance andtolerance, connecting it between an active device such as an opencollector transistor and Vcc, and the transistor's output would bepulled up to Vcc once the transistor is forward biased. With the adventof integrated circuitry, however, fabricating a resistance onto a wafersubstrate, such as silicon or gallium arsenide, takes specialconsideration, particularly when resistivity and tolerances play animportant part in circuit operation.

For example, as SRAMs have evolved from the 4 Kb memory arrays to moredensely packed array sizes, tolerances of pull-up resistances had to betightly controlled. In order to minimize standby current, manyfabrication processes adopted use an active device as the pull-up. InCMOS fabrication, it is common to see a PMOS transistor acting as thecurrent path between a memory cell access transistor and the powersupply bus. In this manner, the PMOS transistor can be gated “on” onlywhen the desired line is to be pulled up to Vcc and turned “off”otherwise. This in essence eliminates leakage current and minimizesstandby current for the SRAM device as a whole.

The main drawback to using an active device for a pull-up device is theamount of space required to fabricate the device. Now that the SRAMgeneration has grown to the 1 Mb array size, die space is a criticalfactor to consider. Technology has basically pushed all types ofintegrated circuits to be more densely packed, and pull-ups are a commonelement in many circuit designs.

Although the invention primarily arose out of concerns associated withresistor fabrication in SRAM circuitry, the artisan will appreciateapplicability of the inventive technology elsewhere, with the inventiononly being limited by the accompanying claims appropriately interpretedin accordance with the doctrine of equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic cross-sectional view of a semiconductor waferfragment at one processing step in accordance with the invention.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a schematic representation of SRAM circuitry in accordancewith an aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention includes several aspects of forming resistor and diodeconstructions. The invention also includes several aspects of SRAM andother integrated circuitry incorporating diodes and resistors producedaccording to the inventive methods, and produced according to othermethods.

A semiconductor processing method of forming a resistor constructionfrom semiconductive material is first described with reference to FIG.1. Such illustrates a bulk semiconductor substrate 12, such asmonocrystalline silicon, having a conductive diffusion region 14 formedtherein. Region 14 constitutes a node to which electrical connection toa resistor is to be made. An electrically insulative layer 16, typicallyborophosphosilicate glass (BPSG), is provided outwardly relative to node14. A first opening 18, preferable in the configuration of asubstantially vertical passageway, is provided therethrough over node14. First opening 18 has an opening width “A”. Node 14 can be providedbefore provision layer 16 and opening 18, or after provision of layer 16and opening 18.

Referring to FIG. 2, a first layer 20 of semiconductive material ischemical vapor deposited over electrically insulative layer 16 andwithin first opening 18 over node 14 to a thickness which is less thanone-half first opening width “A” to less than completely fill firstopening 18 with semiconductive material. Such thereby defines aremaining opening 22. An example semiconductive material of first layer20 is silicon, such as amorphously deposited silicon or polycrystallinesilicon. During or after deposition, first layer 20 can be provided witha first conductivity enhancing dopant impurity of a first “p” or “n”type. Layer 20 can also remain undoped at this point in the process.Accordingly, semiconductive material layer 20 has a first conductivityenhancing dopant concentration falling within a range of from 0 to somefirst value, with the first value typically being less than 1×10¹⁸ions/cm³. Greater values, such as 1×10²⁰ ions/cm³, would effectivelyinherently make layer 20 undesirably sufficiently electricallyconductive to provide negligible resistance effect.

Referring to FIG. 3, a second layer 24 of semiconductive material isprovided by chemical vapor deposition, or other technique, to withinremaining opening 22 and inside of first layer 20 to completely fillremaining opening 22 with semiconductive material. Thus, opening 18 islikewise completely filled with semiconductive material. Second layer 24is provided in one example with a second conductivity dopantconcentration which is greater than the first concentration. Thus, aconductivity enhancing impurity concentration gradient is providedwithin opening 18 which varies from a low concentration at an innerelevation 26 within opening 18 to a higher concentration at an outerelevation 28 within opening 18.

The conductivity enhancing dopants provided in first and second layers20 and 24 can comprise the same or different conductivity “n” or “p”types. Further even if of the same type, the dopants might be different,for example one being arsenic and one being phosphorus which are both“n” type. When of the same type, the semiconductive material effectivelyfilling opening 18 defines a substantially vertically elongated resistorwithin opening/passageway 18, which is an ohmic electrical contact withnode 14. Where the conductivity enhancing dopants provided in first andsecond layers 20 and 24, respectively, are of different type, the resultwill be formation of a substantially vertically elongated diode providedwithin passageway 18 and in ohmic electrical contact with node 14. Thediode will effectively comprise two regions 20 and 24 of semiconductivematerial which in combination completely fill passageway 18.

In such instance, it may be desirable to provide each of regions/layers20 and 24 with about the same concentration level of dopant impurity,and at greater than 1×10²⁰ ions/cm³, to form a highly conductive diode.Alternately, it might be desirable to provide the two regions/layerswith different type and different concentration level dopant impuritiesto effectively define a leaking or leaky diode, which then effectivelyfunctions as a resistor. Accordingly, in one aspect of the invention, aleaky diode construction also constitutes a vertically elongatedresistor within opening 18.

Ultimately, an outer layer of electrically conductive material isprovided outwardly of insulating layer 16 and patterned into aconductive line, with the elongated resistor or diode extending betweennode 14 and the formed conductive line. Such might be accomplished by anumber of methods. For example, the construction of FIG. 3 could beetched back by chemical mechanical polishing, or other means, back tothe upper surface of insulating layer 16. Subsequently, a metal or otherhighly conductive material can be deposited and patterned to form aline. More preferably, second layer 24 of semiconductive material isprovided to have a dopant concentration which is at least 1×10²⁰ions/cm³ and is deposited to a sufficient thickness to enable it to bepatterned into a conductive line 30 (FIG. 4). Accordingly in suchinstance, conductive line 30 comprises both first and second layers 20and 24, with outer layer 24 forming a highly conductive part thereof. Asilicide layer, such as WSi_(x) (not shown), might also be providedoutwardly of layer 24. In either event, the formed diode or resistorextends between node 14 and patterned conductive line 30. Processing inaccordance with the above described preferred method provides theadvantage of provision of a line and diode or resistor without addedmasking steps for the resistor or diode.

Alternate techniques are contemplated for provision of substantiallyelongated vertically oriented resistors or diodes which fillopening/passageway 18. For example in provision of a resistor,opening/passageway 18 might be filled in a substantially continuouschemical vapor deposition step. During such deposition, the conductivityenhancing impurity would be provided to the reactor at a rate varyingfrom, for example, a first lower rate to a second higher rate such thatthe outermost portion of the deposited layer has the desired highconductivity attributes, whereas lower regions have the desiredresistive attributes. The final resultant rate could be provided toproduce a dopant concentration at the outer regions of the depositedlayer which is at least 1×10²⁰ ions/cm³ to facilitate production of adesired highly conductive line outwardly of insulating layer 16.

A similar process could be utilized for formation of a diode. Forexample, a substantially continuous chemical vapor depositing step couldbe utilized to fill passageway/opening 18 and provide a layer thicknessoutwardly of insulating layer 16 sufficient for formation of aconductive line, and define an elongated diode within the passageway.For example, the chemical vapor depositing step could include firstfeeding a conductivity enhancing impurity of a first type into thereactor during deposition to provide semiconductive material of thefirst conductivity type at an inner elevation within the opening. Duringdeposition, the dopant feed to the reactor would be changed from thefirst feeding to a second feeding of a conductivity enhancing impurityof a second type to provide semiconductive material of the secondconductivity type at an outer elevation within the opening. Subsequentprovision of a conductive metal line by mere patterning, or by provisionof other conductive layers and patterning, could be provided.

Alternately in formation of a resistor, semiconductive material might bedeposited atop insulating layer 16 and within opening 18 to beinherently undoped or very lightly doped as-deposited. Subsequently, aconductivity enhancing dopant impurity might be driven into thesemiconductive material layer at least outwardly of the electricallyinsulative layer to a peak concentration of greater than or equal to1×10²⁰ ions/cm³. Subsequently, this semiconductive material layer wouldbe exposed to annealing conditions effective to diffuse dopant impuritywithin the semiconductive material from outwardly of the electricallyinsulative layer into the semiconductive material within the opening toeffectively form an elongated resistor in ohmic contact with node 14.The semiconductive material layer outwardly of the electricallyinsulative layer would thereafter be patterned into a conductive line,with the elongated resistor extending between node 14 and the conductiveline. Example annealing conditions include 950° C. for 20 seconds in anN₂ atmosphere. Alternately, the wafer might be exposed to sufficientthermal conditions throughout processing to inherently provide suchdesired dopant driving to deep within passageway 18.

For diode formation, an alternate process is also contemplated.Specifically, a single semiconductive material layer can be chemicallydeposited to within opening 18 and over layer 16 to completely fill suchopening. As deposited, the semiconductive material layer would beprovided with conductivity enhancing dopant impurity of a first typehaving an average concentration of about 1×10¹⁸ ions/cm³. After thechemical vapor depositing step, a conductivity enhancing dopant impurityof a second type can be provided into the outermost portions of thedeposited layer by ion implantation to a peak and overwhelmingconcentration of at least 1×10²⁰ ions/cm³. The substrate is then exposedto annealing conditions effective to diffuse second type dopant impuritywithin the semiconductive material from outwardly of the electricallyinsulative layer into the first type semiconductive material withinopening 18 to effectively form an elongated diode within the opening.

Integrated circuitry incorporating the above constructions whereby asubstantially vertically elongated resistor or diode extends between anode and an outer conductive line is also contemplated.

FIG. 5 schematically illustrates one example of integrated circuitry ofan SRAM cell in accordance with the invention utilizing at least one ofthe subject resistors. Such comprises a pair of first and secondpull-down transistors 50 and 52, respectively. These include respectivedrains 53, 54; respective sources 55, 56; and respective gates 57, 58.Gate 57 of first pull-down transistor 50 is electrically coupled todrain 54 of second pull-down transistor 52. Likewise, gate 58 of secondpull-down transistor 52 is electrically coupled to drain 53 of firstpull-down transistor 50. A ground node 58 and a Vcc node 60 areprovided. A first resistor 62 and a second resistor 64 electrically arecoupled with Vcc node 60 via a patterned line. Drain 53 of firstpull-down transistor 50 electrically couples with Vcc node 60 throughfirst resistor 62. Drain 54 of second pull-down transistor 52electrically couples through second resistor 64 to Vcc node 60. A pairof cell access transistors 66 and 68 are also provided.

In the context of the previously described construction, the describedand illustrated resistor/leaking diode would constitute one or both ofresistors 62 and 64. Node 14 would constitute one of drains 53 or 54.Node 14 could alternately be the outer surface of gate 57 or gate 58.Patterned line 30 would be configured to extend to the suitable powerVcc node.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

I claim:
 1. Integrated circuitry comprising: an insulative materialprovided over a semiconductive material substrate, the insulativematerial having an opening disposed therein, the opening being generallyelongate and extending downwardly into the insulative material along along axis; the opening terminating on a surface of the semiconductivematerial substrate and having a horizontal axis extending along thesurface of the substrate; the horizontal axis of the opening beingshorter than the long axis of the opening; a first layer ofsemiconductive material having a portion within the opening, the portionof the first layer within the opening extending downwardly along thelong axis of the opening and horizontally along the horizontal axis ofthe opening, the first layer having a longer expanse extendingdownwardly along the long axis of the opening than extendinghorizontally along the horizontal axis of the opening, the first layerhaving a first thickness dimension perpendicular the opening's longaxis; a second layer of semiconductive material having a portion withinthe opening, the portion of the second layer within the openingextending downwardly along the long axis of the opening and horizontallyalong the horizontal axis of the opening, the second layer having alonger expanse extending downwardly along the long axis of the openingthan extending horizontally along the horizontal axis of the opening,the second layer having a second thickness dimension perpendicular theopening's long axis, the first and second thickness dimensions beingdifferent from one another; wherein the first and second layers fill theopening; wherein the first and second layers comprise differentcompositions relative to one another; and the difference in compositionbetween the first and second layers including a difference in dopantconcentration in the first layer relative to the second layer.
 2. Theintegrated circuitry of claim 1 wherein the difference in compositionbetween the first and second layers further includes a difference indopant type in the first layer relative to the second layer.